Online separation and preconcentration of trace heavy metals with 2,6-dihydroxyphenyl-diazoaminoazobenzene impregnated amberlite XAD-4

A rapid and sensitive flow injection online preconcentration method was developed for determination of Cd, Co, Cu, and Zn in natural water samples by flame atomic absorption spectrometry. The procedure is based on the retention of analytes in the form of 2,6-dihydroxyphenyl-diazoaminoazobenzene (DHDAA) complexes on a microcolumn packed with XAD-4-DHDAA resin. Cd, Co, Cu, and Zn can be eluted from the microcolumn with 0.5 mol L-1 HCl and pumped directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). The enrichment factors are 42 ( Cd), 33 ( Co), 28 ( Cu), and 31 ( Zn), for a sample volume of 6.0 mL and 1 min preconcentration time relative to direct introduction of aqueous solutions into an atomic absorption spectrometer. The sampling frequency was 30 h(-1) with a 1 min loading. The proposed method allowed the determination of Cd, Co, Cu, and Zn with detection limits of 0.1, 0.5, 0.3, and 0.2 mu g L-1, respectively. The selectivity of the XAD-4-DHDAA resin for Cd, Co, Cu, and Zn over several electrolytes was also investigated. The method was validated by analysis of a standard reference material (GBW 08301) with the results agreement with those quoted by manufactures. The developed method was applied to the determination of trace Cd, Co, Cu, and Zn in tap water, ground water and river water samples with satisfactory results.